Kindle Direct Publishing (KDP) allows for various formatted documents; however, some formats convert better than others. According to KDP's page on Amazon, the best formats to use are DOC (.doc) and PRC (.prc).
MOBI or PRC is created using the free Mobipocket Creator. Here's the link to this software:
I'll give it a try with my short story collectin "Death By Clogging" which I uploaded the other day to Amazon.com. It's actually easy to upload your book to KDP, but the resulting look is what needs tweaking.
I used Portable Document Format (.PDF) and the result was irregular page breaks and inconsistent text flow. Perhaps Mobicreator will resolve this. I'll let you know soon!